Skills

TRIAC

Description: This is a sensitive gate TRIAC (also known as a thyristor) with a 200V blocking voltage in a bread board friendly TO-92 package. Use a triac to control an AC load (like EL wire, small incandescent lamps, etc) from a DC source (like the GPIO on a microcontroller).

Customer Comments

A triac is a regenerative component. Once it starts conducting above its latching current (which can be as low as 10mA) it won’t stop, even if base voltage goes to zero. To stop it, either interrupt the current running through it, or bypass it momentarily with a pushbutton to eliminate the potential across its main terminals. Of course if it is passing AC, the potential drops to zero each time a positive AC pulse crosses over to become a negative AC pulse, and vice-versa. The triac stops at that instant, and has to be retriggered.

Gate current does not have to “come from the MT2 side.” So long as the gate potential is either higher or lower than the MT1 terminal, the component will start to conduct.

I’m writing a column about the weirdness of triacs for an upcoming Make magazine.

there are a lot of opticouple triacs on the market in roughly the same price range that isolate your circuits better if you are connected to line power. MOC3063, etc. granted they usually are in a bigger form factor because they are this plus an led emmitter/receiver pair. triacs only work to switch AC, DC would only turn on, not off. sparkfun sells a beefier photoisolated triac (http://www.sparkfun.com/products/10636) that would probably be better for most typical applications.

So I wired some EL panels using these (made Simon Says) and I think I’m having the problem you had. First they weren’t working at all (i.e. they wouldn’t turn off), but I reversed their orientation and that fixed it. They worked on two of the four EL panels, but that could be chalked up to sloppy soldering. The bigger problem was when I turned on my inverters, the buttons used in my DC circuit became super sensitive and would randomly trigger. Moral of the story: optical isolators really should be used with these to avoid small leakage currents from finding their way into the DC circuit, even if the AC and DC grounds are tied together.

Triacs a a bit complicated to use in some cases, even though they’re current controlled devices the Gate current must come from the MT2 side of the triac, this page at all about circuits as a good explanation on general triac use. http://www.allaboutcircuits.com/vol_3/chpt_7/6.html

It works like a latching switch, you turn it on by putting some voltage on the gate lead, and then it turns on, conducting between the main terminals. It stays on
until the current between the main terminals drops to zero (which is why they work well with AC, which drops to zero twice every cycle). To connect it to control EL wire, put the triac in series with your EL wire. Works fine with an MCU, just ground your MCU to one main terminal, and connect an I/O pin to the gate via a small resistor.

Note, if your EL supply is high voltage and you don’t want to tie it to your MCU ground, you can use an opto-isolator to drive the triac. I do it this way a lot, especially when I’m using the triac to switch mains voltage.

Customer Reviews

SparkFun is an online retail store that sells the bits and pieces to
make your electronics projects possible. Whether it's a robot that can
cook your breakfast or a GPS cat tracking device, our products and
resources are designed to make the world of electronics more accessible.

In addition to products, SparkFun also offers
classes and online tutorials to help educate
individuals in the wonderful world of embedded electronics.